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UC1526: Regulating Pulse width Modulator having Low Switching Frequency

Ramana Murthy
Expert 1765 points
Part Number: UC1526
Other Parts Discussed in Thread: DRV8801

i am trying to use Regulating pulse width modulator UC1526 in DC to DC Converter(Buck Conv).

I need to generate Initial 20 to 30 Sec Ramp in Duty cycle to Provide soft start to DC motor at Starting(to limit Starting current).

Where should i actually provide positive ramp from my analog circuit to UC1526 Error amplifier of  inverting terminal or Non inverting...?

Please tell me how Duty Cycle exactly depends on  feedback Voltage.

My DC - DC Converter operating frequency =5 KHZ

I am planing to provide positive ramp to Error +(Reference) Terminal of UC1526 and Later I will Maintain Constant Reference  5V after Ramp of 20Sec

as usual resistor divider Feedback i will be given to (Error -) ...It will Work..?

Please you can suggest me better IC for Application

  • 0
    TI__Expert 7445 points
    Hi Anand,

    UC1526 has a built in soft start function. Thus adding a capacitor from pin 4 Css to gnd. As highlighted in the datasheet pg. 4 under Soft –Start Circuit. “ As the soft-start voltage ramps up to +5V, the duty cycle of the PWM linearly increases.”
    Will investigate if there are other IC that can be recomended.
  • 0 in reply to Ramesh Khanna
    Expert 1765 points
    Hello Ramesh Sir,

    But it can provide 30sec Ramp.....I Thought it only provide 30msec Ramp.....
    please suggest me the capacitor Value for 30sec Ramp if it Supports...
    otherwise please suggest me Best Suitable IC for my Application....
    My IDEA:
    I am planing to provide positive ramp to Error +(Reference) Terminal of UC1526 and Later I will Maintain Constant Reference 5V after Ramp of 20Sec
    is it work...?
  • 0 in reply to Ramana Murthy
    TI__Expert 7445 points
    Hi Anand,

    As highlighted in the soft start section you would have a current source charging the capacitor. Yes for 20-30 sec capacitance value will be high.

    There are dedicated controllers for the motor drive i.e DRV8801 etc.
    Is your application for space or commercial.
    Link below will provide you various options.
    www.ti.com/.../products.html